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    <title>Document</title>
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    <script>
      const arr = [1, 2, 3, 2, 9]
      const res = arr.reduce(function (newArr, item) {
        if (newArr.indexOf(item) === -1) {
          newArr.push(item)
        }
        return newArr
      }, [])
      console.log(res)

      // 方法二： Set 直接去重 返回一个对象； 展开添加到数组
      // const newArr = new Set(arr)
      // console.log([...newArr])
    </script>
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